The subject matter of the present invention relates to a novel method of perforating a formation traversed by a wellbore in a single run using a long perforating gun string that is longer than a wellhead lubricator, where the long gun string used in connection with the aforementioned novel method of perforating includes an automatic release apparatus which is adapted to be connected between adjacent perforating guns of the long gun string or between a firing head and a perforating gun of the long gun string, the automatic release apparatus automatically separating into a first top piece and a second bottom piece in response to a detonation wave propagating through the release apparatus, initiation of the automatic separation taking place before the perforating guns of the long gun string detonate, the perforating guns of the long gun string located below the second bottom piece of the automatic release apparatus falling to a bottom of the wellbore when the automatic release apparatus separates into the two pieces and the perforating gun connected to the second bottom piece of the release apparatus detonates.
In application Ser. No. 08/032,817 filed Mar. 16, 1993, now U.S. Pat. No. 5,293,940 which is a continuation of application Ser. No. 07/858,400 filed Mar. 26, 1992 abandoned, an automatic tubing release apparatus adapted to be disposed in a wellbore includes a frangible member and enclosed detonating cord. The frangible member shatters when a detonation wave, propagating in the detonating cord, passes through the frangible member. Before the frangible member shatters, a perforating apparatus is connected to an interior of a tubing. However, when the frangible member shatters, the perforating apparatus is automatically released from the interior of the tubing and the perforating apparatus falls to a bottom of the wellbore.
In application Ser. No. 07/955,816 filed Oct. 2, 1992, now U.S. Pat. No. 5,318,126 which is a contination of the aforementioned application Ser. No. 07/858,400 filed Mar. 26, 1992 which was abandoned and became Ser. No. 08/032,817 filed Mar. 16, 1993, now U.S. Pat. No. 5,293,940 an explosively opened production valve adapted to be disposed in a wellbore includes the same frangible member with enclosed detonating cord adapted to conduct a detonation wave. The production valve is initially disposed in one state (e.g, a closed state). However, when the frangible member shatters in response to the detonation wave, conducting in the detonating cord, passing through the frangible member, the production valve changes from the one state to another state (e.g., an open state).
In application Ser. No. 08/057,948 filed May 5, 1993, now U.S. Pat. No. 5,366,013 which is a contination in part of the aforementioned application Ser. No. 07/955,816 filed Oct. 2, 1992, now U.S. Pat. No. 5,318,126, a shock absorber adapted to be disposed in a wellbore includes the same frangible member with enclosed detonating cord adapted to conduct a detonation wave. The shock absorber initially cannot absorb shock. However, when the frangible member shatters in response to the detonation wave passing through the frangible member, the shock absorber is then ready to absorb shock.
In application Ser. No. 08/220,983 filed Mar. 30, 1994, which is a continuation in part of the aformentioned application Ser. No. 08/057,948 filed May 5, 1993, now U.S. Pat. No. 5,366,013 a wellbore tool includes a means for expanding an anchor slip which grips a wellbore casing and a primary anchor release mechanism for automatically releasing the anchor slip when the same frangible member shatters in response to a detonation wave propagating in a detonating cord.
In all of the aforementioned applications, a detonating cord is enclosed by a frangible member. When a detonation wave propagates within the detonating cord, the detonation wave passes through the interior of the frangible member. In response to the detonation wave, the frangible member shatters. When the frangible member shatters, an event occurs.
It is common practice to perforate wellbores by using a perforating gun which suspends by a wireline in the wellbore. However, for a single run in the wellbore, the weight of the perforating gun is a function of and limits the length of the perforating gun string due to the breaking strength of the wireline. That is, for a single run in the wellbore, when a perforating gun string suspends by wireline in a wellbore, if the length of the perforating gun string is longer than a wellhead pressure lubricator, when the perforating gun detonates, the shock of the perforating gun will sometimes snap and break the wireline. Therefore, in order to avoid this problem, when a long length interval in the wellbore (i.e., longer than a wellhead pressure lubricator) must be perforated, several separate wireline perforating runs in the wellbore was required. For example, after a first zone in the wellbore was perforated, the well became pressurized. The old wireline perforating gun string section was removed in order to attach the next new perforating gun string section. The old wireline perforating gun string section was raised into a wellhead pressure lubricator (sometimes called a riser) and a valve below the lubricator was closed. Pressure was bled from the lubricator, the lubricator was detached, the next perforating gun string section was attached to the wireline, and a wellhead pressure lubricator was reattached to the wellhead. The valve was then opened and the new wireline perforating gun string section was run back into the wellbore, under pressure, in order to perforate a second zone in the wellbore.
However, it is expensive and time consuming to perforate a long length interval of a wellbore (i.e., an interval in the wellbore which is longer than a wellhead lubricator) by performing the aforementioned several separate wireline perforating runs in the wellbore. It would be more convenient, less time consuming, and less expensive to perforate the long length interval in the wellbore during a single run in the wellbore while maintaining underbalance, without resorting to the several separate wireline perforating runs, without breaking or snapping the wireline, and without killing the well.
This can be accomplished by using a novel perforating method and, during the practice of the novel perforating method, by using a perforating gun string that includes a novel automatic release apparatus. The automatic release apparatus would initiate disconnection of a first part of a long perforating gun string (a gun string which is longer than the wellhead lubricator) from a second part of the gun string, which includes a perforating gun, immediately before detonating the perforating gun of the second part. This would reduce the shock of the long gun string on the wireline. This reduction of the shock of the gun string on the wireline would prevent the gun string from snapping and breaking the wireline. As a result, by using the novel perforating method and the novel automatic release apparatus of the present invention, one can perforate a long length interval in the wellbore during a single run into the wellbore by using a long perforating gun string which is longer than the wellhead lubricator without snapping and breaking the wireline while maintaining underbalance and without killing the well; it would not be necessary to practice the old, more expensive method of performing several separate wireline perforating runs into the wellbore.
U.S. Pat. No. 5,293,940 to Hromas et al discloses an Automatic Tubing Release apparatus. However, this apparatus is adapted to be connected between a perforating gun and a tubing string and includes a collet finger which is attached to an internal surface of a fill sub which is connected to the tubing string. A release of the collet finger from the internal surface of the fill sub releases the perforating gun from the tubing string. However, this automatic release apparatus, by design, must be connected between the perforating gun and the tubing string. It cannot be connected between adjacent perforating guns of a long perforating gun string run on wireline. Therefore, the release apparatus of the above Hromas et al patent cannot be used in connection with a long wireline perforating gun string for perforating long length intervals in a wellbore in a single perforating run. Another new automatic release apparatus design is needed.